Currently, thermosetting protective and decorative coatings are generally applied to metal strip or sheet for packaging end uses by roller-coating of a solvent-based lacquer (which may comprise water and a co-solvent) typically comprising 30-60% by weight solids. After application of the lacquer to the metal strip or sheet, the solvent is removed by evaporation and the applied coating is cured. For cost and environmental reasons, it would be desirable to be able to reduce the usage of organic solvents in the application of thermosetting coatings, and the present invention is directed to that objective.
U.S. Patent Specification No. 4,990,364 describes solvent-free, low monomer or monomer-free polymerisable or curable compositions for use in coating various classes of substrates, including metal substrates for packaging end use. The compositions are indefinitely stable under the conditions described and are curable only by means of free-radical initiators in conjunction with heat treatment; by means of actinic light, especially ultra-violet radiation; or by electron radiation. There is no disclosure of thermally activated crosslinkable systems.